Lubricant composition containing phenothiazine and dipyridylamine



United States Patent LUBRICANT COMPOSITION CONTAINING PHE- Thisapplication is a continuation-in-part of my application Serial No.34,375, filed June 7, 1960, now abandoned.

This invention relates to ester-based lubricant compositions containinga novel combination of base oil-soluble additive agents. Moreparticularly, the present invention relates to ester-based syntheticlubricant compositions which exhibit increased oxidation resistance.

Organic compounds, such as lubricating oils, undergo oxidation uponexposure to air. This process is accentuated by elevated temperaturessuch as occur in engines and other operating machinery. When suchorganic compositions are used as motor or machinery lubricants, theirstability is still further drastically reduced due to their contact withmetal surfaces which give up metallic particles to the lubricant. Suchabraded or dissolved metals or metal salts appear to act as oxidationcatalysts in the lubricant causing the formation of primary oxidationproducts which in turn cause further degradation of the organiccompounds present in the composition. In addition, water also causescorrosion of metallic surfaces and accentuates oxidation of thelubricant.

Problems of this nature are encountered in mineral oils but appear to beparticularly troublesome in synthetic oleaginous fluids exemplified byesters. Ordinarily, these synthetic ester fluids can be effectivelyinhibited against oxidation by the us of small amounts of additives.However, in the presence of certain metals and metal compounds oftenoccurring in the lubricants, particularly as aforementioned, throughcontact with metal surfaces such as iron, the effectiveness of theadditives is greatly reduced.

The present invention provides a synthetic ester-based lubricantcontaining phenothiazine and dipyridylamine.

If desired, there may also be added to the composition of the presentinvention a minor amount of aminoquinoline, aminopyridine or mixturesthereof. The additives of the present invention are used in minoramounts suflicient to retard oxidation of the lubricants at temperaturesin excess of 400 F. even when the lubricant contains oxidation-promotingconcentrations of iron. Iron as used in the present invention includesmetallic iron and inorganic and organic compounds of iron acknowledgedas oxidation catalysts.

The phenothiazine-dipyridylamine additive combination of the presentinvention provides ester-based fluids with excellent oxidationresistance but in the presence of metal contaminants such as iron,larger amounts of the phenothiazine and/ or dipyridylamine may beneeded, the exact amount depending on the particular base fluidemployed, the amount of metal present, etc. In these cases, the largeramount 'of dipyridylamine or phenothiazine can be replaced in part withaminopyridine or aminoquinoline. In any event it is preferred to have atleast about 0.3 or even 0.5% by weight of each inhibitor used on a totalinhibitor concentration of at least about 1.5% or even at least about 2%by Weight of the final composition.

The phenothiazine of the present invention can be present in amounts ofabout .01 to 5 percent by weight of the final composition with apreferred amount being from about 0.3 or 0.5 to 2% and the phenothiazinemay be substituted as with alkyl groups. The dipyridylamine 3,226,324Patented Dec. 28, 1965 additive can be ring-substituted, as for examplewith alkyl groups, and can be present in amounts from about 0.10 to 5percent by weight of final composition, preferably about 0.3 to 2 weightpercent. The preferred dipyridylamine is 2,2-dipyr'idylami'ne.

The preferred aminoquinolines for use in the present invention are3-arninoquinoline and 8-aminoquinoline and their ring-substitutedderivatives, e.g., alkyl-substituted. Among the useful aminopyridinesare 2-aminopyridine and the ring-substituted, e.g., alkyl-substituted,aminopyridines. The aminoquinolirres or aminopyridines when employed,can be added in amounts from about .01 to 5% by weight of the finalcomposition with the preferred amount being from about 0.3 or 0.5 to 2%by weight of the final composition. The aminoquinoline or aminopyridineadditive is normally added to the ester-based lubricant along with thephenothiazine. For best results the relative concentrations of theadditive will vary with the particular ester lubricant employed and willalso be dependent upon the characteristics of the final lubricantcomposition desired. Normally it is preferred that at least about 1.5parts of dipyridylamine and at least about 0.5 part of aminoquinoline oraminopyridine, when employed, to 1 part of phenothiazine be used.Increasing the amounts of dipyridylamine, aminoquinoline oraminopyridine will generally be beneficial.

The lubricant composition of this invention includes as the majorcomponent a base oil which is an ester of lubricating viscosity whichmay be, for instance, a simple ester or compounds having multiple estergroupings, such as complex esters, polyesters or diesters. These estersare made from monoand polyhydroxy aliphatic alcohols and aliphaticcarboxylic acids, frequently of about 4 to 12 carbon atoms; aliphaticincluding cycloaliphatic. It is preferred that the terminal ester monohydric alcohol residues of these fluids be of a non-neomonohydricalcohol, i.e., contains at least one hydrogen atom on the beta carbon.Ester fluids having terminal alcohol groups provided by neo-monohydricalcohols, i.e., an alcohol whose beta carbon atom contains no hydrogenatoms, have been found to be easily inhibited against oxidation byphenothiazine and little protection beyond that aflorded byphenothiazine alone may be obtained upon addition of the dipyridylaminecomponent. In the cases where the lubricant was easily inhibited withphenothiazine alone, the terminal alcohol groups also contained atertiary hydrogen atom.- The reaction product of a monohydroxy alcoholand a monocarboxylic acid is usually considered to be a simple ester. Adiester is usually considered to be reaction product of 1 mole of acarboxylic acid, say of 6 to 10 carbon atoms, with 2 moles of amonohydric alcohol or 1 mole of a glycol of 4 to 10 carbon atoms Withtwo moles of a moncarboxylic acid of 4 to 10 carbon atoms. The diestersfrequently contain from 20 to 40 carbon atoms. One complex ester is ofthe type in which X represents a monohydric alcohol residue, Yrepresents a dicarboxylic acid residue and Z represents a glycol residueand the linkages are ester linkages. Those esters, wherein X representsa monoacid residue, Y represents a glycol residue and Z represents adibasic acid residue are also considered to be complex esters. Thecomplex esters often have 30 to 50 carbon atoms. Polyesters, orpolyester, bright stocks can be prepared by direct esterification ofdibasic acids with glycols in about equirnolar quantities. Thepolyesterification reaction is usually continued until the product has akinematic viscosity from about 15 to 200 centistokes at 210 F., andpreferably 40 to centistokes at 210 F.

Although each of these products in itself is useful as a lubricant, theyare particularly useful when added or blended with each other insynthetic lubricant compositions. These esters and blends have beenfound to be especially adaptable to the conditions to which turbineengines are exposed, since they can be formulated to give a desirablecombination of high flash point, low pour point, and high viscosity atelevated temperatures, and need contain no additives which might leave aresidue upon volatilization. In addition, many complex esters have showngood stability to shear. Natural esters, such as castor oil may also beincluded in the blends, as may be up to about 1 percent or more byweight of a foam inhibitor such as a methyl silicone polymer or otheradditives to provide a particular characteristic, for instance, extremepressure or load carrying agents, corrosion inhibitors, etc., can beadded.

Typical synthetic lubricants may be formulated essentially from a majoramount (about 6085%) of a complex ester and a minor amount (about 40%)of a diester, by stirring together a quantity of diester and complexester at an elevated temperature, altering the proportions of eachcomponent until the desired viscosity is reached. Polyesters can beemployed to thicken diester base stocks to increase the load carryingcapacity of the base diester oil. The polyester will generally notcomprise more than about 50 weight percent of the blend, preferablyabout to 35 weight percent. Usually the amount of the polyester employedin any blend would be at least about 5 percent, and the majority of thelubricant is a diester. Other polymers such as Acryloids may be added asthickeners to the esters, generally the simple esters such as the abovediesters, to obtain a base oil of desired viscosity. The Acryloids arepolymers of mixed C to C esters of methacrylic acid having 10,000 to20,000 molecular weight. Advantageously the final lubricating oilcomposition would have a maximum viscosity at -40 F. of about 13,000centistokes and a minimum viscosity of about 7.5 centistokes at 210 F.

The monohydric alcohols employed in these esters usually contain lessthan about 20 carbon atoms and are generally aliphatic. Preferably thealcohol contains up to about 12 carbon atoms and is of a non-neostructure at the beta carbon atom, i.e., has at least one hydrogen onthe beta carbon atom. Useful aliphatic alcohols include butyl, hexyl,methyl, iso-octyl and dodecyl alcohols, C OX0 alcohols and octadecylalcohols. C to C branched chain primary alcohols are frequently used toimprove the low temperature viscosity of the finished lubricantcomposition. Alcohols such as n-decanol, 2- ethylh-exanol, oxo alcohols,prepared by the reaction of carbon monoxide and hydrogen upon theolefins obtainable from petroleum products such as diisobutylene and Colefins, ether alcohols such as butyl carbitol, tripropylene glycolmono-isopropyl ether, dipropylene glycol mono-isopropyl ether, andproducts such as Tergitol 3A3, which has the formula C H O(CH CH O) H,are suitable alcohols for use to produce the desired lubricant.Iso-octanol and iso-decanol are alcohol mixtures made by the 0x0 processfrom C to C copolymer heptenes. The cut which makes up isa-octanolusually contains about 17% 3,4-dimethylhexanol; 29% 3,5-dimethylhexanol;4,5-dimethylhexanol; 1.4% 5,5- dimethylhexanol; 16% of a mixture of3-methylheptanol and S-ethylheptanol; 2.3% 4-ethylhexan0l; 4.3% oc-alkylalkanols and 5% other materials.

Generally, the glycols contain from about 4 to 12 carbon atoms; however,if desired they could contain a greater number. Among the specificglycols which can be employed are 2-ethyl-1,3-hexandiol 2propyl-3,3-heptanediol, 2-rnethyl 1,3 pentanediol, 2-butyl-1,3- butanediol,2,4-diphenyl-1,3-butanediol, and 2,4-dirnesityl-1,3-butanediol. Inaddition to these glycols, other glycols may be used, for instance,where the alkylene radical contains 2 to 4 carbon atoms such asdiethylene glycol, dipropylene glycol and other glycols up to 1000 to2000 molecular weight. The most popular glycols for the manufacture ofester lubricants appear to be polypropylene glycols having a molecularweight of about 300 and 2-ethyl hexanediol. The 2,2-dimethyl glycols,such as neopentyl glycol have been shown to impart heat stability to thefinal blends. Minor amounts of other glycols or other materials can bepresent as long as the desired properties of the product are not undulydeleteriously affected.

Aside from glycols, the esters may be made from polyhydric alcohols ofmore than two hydroxyl groups, e.g. triand tetrahydroxy aliphaticalcohols having about 4 to 12 carbon atoms, preferably about 5 to 8carbon atoms; for instance pentaerythritol, trimethyolpropane and thelike. Particularly suitable ester base oils are formed when thesealcohols are reacted with monocarboxylic acids having about 4 to 12carbon atoms, preferably 4 to 9 carbon atoms. It is preferred that thereaction be conducted so as to substantially completely esterify theacids.

One group of monocarboxylic acids includes those of 8 to 24 carbon atomssuch as stearic, lauric, etc. The carboxylic acids employed in makingester lubricants will often contain from about 4 to 12 carbon atoms.Suitable acids are described in US. Patent No. 2,575,195 and include thealiphatic dibasic acids of branched or straight chain structures whichare saturated or unsaturated. The preferred acids are the saturatedaliphatic carboxylic acids containing not more than about 12 carbonatoms, and mixtures of these acids. Such acids include succinic, adipic,suberic, azelaic and sebacic acids and isosebasic acid which is amixture of a-ethyl suberic acid, a,a'-diethyl adipic acid and sebacicacid. This composite of acids is attractive from the viewpoint ofeconomy and availability since it is made from petroleum hydrocarbonsrather than the natural oils and fats which are used in the manufactureof many other dicarboxylic acids, which natural oils and fats arefrequently in short supply. The preferred dibasic acids are sebacic andazelaic or mixtures thereof. Minor amounts of adipic used with a majoramount of sebacic may also be used with advantage.

Various useful ester base oils are disclosed in U.S. Patent Nos.2,499,983, 2,499,984, 2,575,195, 2,575,196, 2,703,811, 2,705,724 and2,723,286. Generally, the synthetic base oils consist essentially ofcarbon, hydrogen and oxygen, i.e., the essential nuclear chemicalstructure is formed by these elements along. However, these oils may besubstituted with other elements such as halogens, e.g., chlorine andfluorine. Some representative components of ester lubricants are ethylpalmitate, ethyl stearate, di(Z-ethylhexyl) sebacate, ethylene glycoldilaurate, di(Z-ethylhexyl) phthalate, di(1,3-methyl butyl) adipate,di-(Z-ethyl butyl) adipate, di(l-ethyl propyl) adipate, diethyl oxylate,glycerol tri-n-octoate, di-cyclohexyl adipate, di-(undecyl) sebacate,tetraethylene glycol-di-(Z-ethylene hexoate), di-Cellosolve phthalate,butyl phthallyl butyl glycolate, di-n-hexyl fumarate polymer,- dibenzylsebacate, and diethylene glycol bis (Z-n-butoxy ethyl carbonate).Z-ethylhexyl-adipate-neopentyl glycyladipate-Z-ethylhexyl, is arepresentative complex ester. Generally, these synthetic esterlubricants have a viscosity ranging from light to heavy oils, e.g.,about 50 SUS at 100 F. to 250 SUS at 210 F., and preferably 30 to SUS at210 F.

The esters are manufactured, in general, by mere reaction of thealcoholic and acidic constituents, although simple esters may beconverted to longer chain components by transesterification. Theconstituents, in the proportions suitable for giving the desired ester,are reacted preferably in the presence of a catalyst and solvent orwater entraining agent to insure maintenance of the liquid state duringthe reaction. Aromatic hydrocarbons such as xylene or toluene haveproven satisfactory as solvcnts. The choice of solvent influences thechoice of temperature at which the esterification is conducted; forinstance, when toluene is used, a temperature of 140 C. is recommended;with xylene, temperatures up to about 195 C. may be used. To provide abetter reaction rate an acid esterification catalyst is often used. Manyof these catalysts are known and include, for instance, HCl, H 50 NaHSOaliphatic and aromatic sulfonic acids, phosphoric acid, hydrobromicacid, HF and dihydroxyfluoboric acid. Other catalysts are thionylchloride, boron trifiuoride and silicon tetrafluoride. Titanium estersalso make valuable esterification and transesterification catalysts.

In a preferred reaction, about 0.5 to about 1 weight percent, oradvantageously, 0.2 to 0.5% of the catalyst is used with xylene solventat a tempertaure of 165 to 200 C. while refluxing water. Thetemperatures of the reaction must be sufficient to remove the water fromthe esterification mass as it is formed. This temperature is usually atleast about 140 C. but not so high as to decompose the wanted product.The highest temperature needed for the reaction will probably be about200 C., preferably not over about 175 C. The pressure is convenientlyabout atmospheric. Although reduced pressure or superatmosphericpressure could be utilized. there is usually no necessity to use reducedpressures, as the temperatures required at atmospheric pressure toremove the water formed do not usually unduly degrade the product.

When reacting glycols with dibasic acids to produce a polyester, it ispreferred to continue the reaction with concomitant boiling off of waterfrom the reaction mixture until the polyester product has a kinematicviscosity of about 15 to 200 centistokes at 210 F., preferably about to130 centistokes. When this point has been reached, the polymerizationcan be stopped, for instance, by adding a capping alcohol to thereaction mixture, and continuing to reflux until water ceases to beevolved. The capping alcohol is a low molecular weight monoalcohol of upto about 20 carbon atoms. It is standard practice, when esters are madeusing the conventional acid catalysts such as sodium bisulfate orparatoluenesulfonic acid to give the esters an after-treat by washingthe ester with a 5 percent aqueous K CO solution or by heating the esterin an autoclave for 15 hours at 340 TABLE I.RESULTS OF OXYGEN ABSORPTIONTESTS [Conditionsz 450 F.; 1 it. O /hr.; g. fluid] R Cone. (Wt.Induction Total time Volume of 0 N 0. Base fluid Additives percent)period (min) absorbed (min) (1111.)

Base oil A None- 5 119 3, 000 1 d Phenothiazine 1. 0 205 247 2, 500 2 doHugo-.- 117 146 2,500

o- 3 {3-aminoquinoline. O. 5 563 500 Phcnothiazine 0. 5 4 d3-aminoquin0line 0. 5- 84 147 2, 500

Iron oetoate 083 Phenothiazinei 5 3-arninoquino ne 5 52,2-dipyridylamine 1. 0 465 Iron oetoate 083 2,2'-dipyridylamine 2. 0 935 1, 056 3-aminoquinoline 1. 0 10 82 2, 500 P fi d0h g 114 134 1, 320

eno iazine- {Z-amlnopyridine. 0. 5 i 305 361 500 Phenothiazine 0. 6Z-aminopyridine 0. 5 195 245 2, 500 Iron oct0ate 083 ghenothiaziriie g-am1no yri 1ne 2,2-dipy i'idylamine 1. 0 522 Iron oetoate 083 12 doialminfipyridine 8 15 31 660 eno razrne- 2,2-dipyridylamine 1. 0 i 21500Phenothiazine 1. 0 14 do 2,2-dipyridylarnine 1. 0 *572 2, 500

glen oectipate 283 139 Trimeth 101- ro ane eno iazine.

pelargd nate f p 3-aminoquinoline. 5 318 354 500 Phenothiazine 5 2s3 doS-aminoquinoline. 5 301 335 2, 500

2,2-d.ipyridylamine 1. 0 lghenothiagine g -am1noqu1no me.[2,2-d.ipyridylamine 1. 0 538 560 Iron oetoate 083 Phenothiazine. 5 316Oil B 3 3-amiuoquinoline- 5 *474 1, 190

2,2-dipyridylamine 1. 0 l1$l0th1a2in% g -a noquino ne-2,2-dipyridylamine 1. 0 482 980 Iron oetoate 083 Phenothiazine. 5 318 do2-arnin0pyridine- 5 *481 1, 035

2,2-d ipyridy1amine 1. 0 Phenothiazige- 5 2-aminopyri ine- 52,2-dipyridylamine 1. 0 474 690 Iron oetoate 0. 083 Phenothiazine 0. 2216 248 2, 500 g0- 311 352 2,500 0...- {2,2-d.ipyridylamine 0. 3 193 212500 Phegethiazine 8 283 330 2, 500 0 {2,2-dipyridylam ine 1. 0 i 338 36521 5 An ester from pentaerythritol and a mixture of aliphaticmonoearboxylic acids with an average chain length of seven carbon atoms.F., 28.4 cs.

2 A concentrate of iron oetoate in mineral oil containing 6.0% iron. 3An ester from trirnethylolpropane and a mixture of Valerie and pelarAcid No. 0.03; sap. No. 372; K.V. at 10 F., 3.41 cs.; K.V. at100 F.,14.4 cs

*The test was stopped at this point. The end of the induction period hadnot been reached, however. 4 Bis(2,2,4-trimethyl-pentyl) sebacate. Itshould be noted that Runs 3 to 5 with this oil were conducted in adiiicrent apparatus where the test is more severe for some unknownreason.

Typical inspection data: Acid No. 0.01; sap. No. 400; K.V. at 210 F.,5.30 cs.; K.V. at

gonic acids. Typical inspection data:

to 350 F. with 10 weight percent of propylene oxide. It is alsoconventional to subject the ester to filtration to remove insolublematerials. After this the product may be subjected to a reduced pressuredistillation or stripping at 100 to 200 C. to remove volatile materials,such as water, the solvent and light ends.

Samples of ester fiuids with and without phenothiazine andaminoquinoline or amino-pyridine and samples made according to thepresent invention were subjected to oxygen absorption tests at 450 F.The tests were conducted by passing a stream of oxygen at the rate ofone cubic foot per hour through 75 grams of the ester fluid containingthe inhibitors and comparing the amount of oxygen absorbed vs. time. Theinduction period is the time in which little or no oxygen is absorbed bythe fluid. The end of the induction period is signaled by a markedincrease in the rate of oxygen absorption. The results of these testsare shown in Table I.

The data in Table I demonstrate the advantageous oxidation resistanceprovided by the addition of phenothiazine and dipyridylamine tosynthetic ester fluids. The data also show the ability of the additivesof the present invention in overcoming the adverse eflfects of ironsalts on inhibitor life and to prevent oxygen up-take for a far longerperiod of time.

A synthetic ester fluid containing the inhibitor combination of thepresent invention was also subjected to the ERDCOWADC Bearing Rig Headmounted on an ERDCO Universal Tester. For comparison a sample containingphenothiazine and aminoquinoline was also tested.

The test conditions and results are listed in Table II.

Conditions Duration 100 hours Test bearing speed 10,000i100 r.p.m.

Test bearing load 500 radial Test bearing temperature 500i10 F.

Test oil temperature 400i10 F.

Test oil sump temperature 440i F.

Test oil flow 600 ml./min.

Air flow 15,000 cc./rnin.

Results:

3 Example 11 Parts by wt. Plexol255 1 98.75

Phenothiazine 0.5 Glycol titanate polymer 0.25 3-aminoquinoline orZ-aminopyridine 0.5 2,2-dipyridylamine 1.0 Sebacic acid .0075 D.C.F.20060,000 .001

A mixture of diisooctyl adipate, di-tridecyl sebacate and Acryloid-DGG(a copolymer of alkyl methacrylates and N-vinyl pyrolidone) 2 SecExample I.

Example II! Parts by wt. Diisooctyl azelate 25.5 Complex ester 1 74.0Phenothiazine 0.5 Free azelaic acid 0.01 3-arninoquinoline orZ-aminopyridine 0.5 2,2-dipyridylamine 1.0

D.C.F. ZOO-60,000 0.001

1 Derived from the reaction of one mole of neopentyl glycol, 2 moles ofazelaic acid and two moles of isooctyl alcohol.

I claim:

l. A lubricant composition consisting essentially of an ester-basedsynthetic fluid of lubricating viscosity, about 0.01 to 5% by Weight ofphenothiazine and about 0.01 to 5% by weight of dipyridylamine andsuflicient to retard oxidation of said ester based synthetic fluid attemperatures in excess of 400 F., said ester based fluid being an esterof an alkanol of 4 to 12 carbon atoms and an alkane carboxylic acid of 4to 12 carbon atoms.

2. The composition of claim 1 wherein the dipyridylamine is2,2-dipyridylamine.

3. The lubricant composition of claim 2 to which is added about 0.3 to5% by weight of a material selected from the group consisting ofaminoquinoline and aminopyridine.

4. The lubricant composition of claim 3 containing about 0.3 to 2% byweight of 2,2'-dipyridylamine, about 0.3 to 2% by weight ofphenothiazine and about 0.3 to 2% by weight of 3-aminoquinoline.

TABLE II.RESULTS OF ERDCO-WADC HIGH TEMPERATURE BEARING RIG Test BaseCone. (wt. Initial K.V. Final K.V. Initial Final No. fluid Additivespercent) at 100 F. at 100 F. acid N0. acid No.

14. on A. 2s. 190. 2 0. 04. 8.50

Phenothiazine 5 15 .do. 3-aminoquinolinc 5 26. 23 75. 27 0.02 5. 64

2,2-dipyridylamine 1. 0

The change in viscosity and acid number of the fluid during a test is ameasure of the effectiveness of the inhibitors. As the results show, theviscosity of the fluid containing dipyridylamine increases very littleas compared to a fluid which did not contain the dipyridylamine.

Other examples of formulations within the present invention are asfollows:

A diethylhexyl sebacate oil having a kinematic viscosity at 100 F. of12:3 cs., a viscosity index of 154, a pour point of below -80 F. andacid N0. of 0:12.

A polymer derived from tetrabutyl titanate and 2-ethyl- 1,3-liexanedi0l.

3 D.C.F. 200 00.000 is a methyl silicone polymer having a viscosity of60,000 cs. at 25 C. and is an anti-foaming agent.

5. A lubricant composition consisting essentially of an ester-basedsynthetic fluid of lubricating Viscosity, about 0.01 -to 5% by weight ofphenothiazine, about 0.01 to 5% by weight of dipyridylamine andsuflicient to retard oxidation of said ester-based synthetic fluid attemperatures in excess of 400 F., said ester-based fluid being an esterof an alkanol of 4 to 12 carbon atoms and an alkane carboxylic acid of 4to 12 carbon atoms which ester has terminal monohydric alcohol residuescontaining at least one hydrogen atom on the beta carbon atom.

6. A lubricant composition consisting essentially of an ester-basedsynthetic fluid of lubricating viscosity, about 0.3 to 2 weight percentof phenothiazine, about 0.3 to 2 percent of 2-aminopyridine and about0.3 to 2 weight percent of 2,2-dipyridylamine, said ester-based fluidbeing an ester of an alcohol of 4 to 12 carbon atoms and an alkanecarboxylic acid of 4 to 12 carbon atoms.

'7. The lubricant composition of claim 6 in which the ester has terminalmonohydric alcohol residues containing at least one hydrogen atom on thebeta carbon atom.

8. The lubricant composition of claim 1 to which is 9 added about 0.1 to5% by weight of a material selected from the group consisting ofaminoquinoline and aminopyridine.

9. The lubricant composition of claim 8 in which the ester has terminalmonohydric alcohol resides containing at least one hydrogen atom on thebeta carbon atom.

10. The composition of claim 8 wherein the dipyridylamine is2,2'-dipyridylamine.

References Cited by the Examiner UNITED STATES PATENTS 2,136,788 11/1938Fairlie 252401 2,198,961 4/1940 Dietrich 252401 2,318,196 5/1943Chenicek 252-401 2,948,680 8/ 1960 Fields 4463 2,961,406 11/1960 McNeil25256 3,038,858 6/1962 Verley 25247 10 3,048,542 8/1962 Tierney et al.25247.5 3,078,230 2/1963 Cyba 252401 FOREIGN PATENTS |786,767 11/1957Great Britain.

OTHER REFERENCES Atkins et al., Development of Additives and LubricatingOil Compositions, I. and E. Chem. 39, 491-493 (No. 4, April 1947 Cole etal.: Survey of the Literature on Antioxidants and AnticorrosionAdditives for Lubricants at Elevated Temperatures, WADC Technical Report53-353 (1954), Wright Air Development Center, Wright-Patterson Air ForceBase, Ohio, page 62 pertinent.

DANIEL E, WYMAN, Primary Examiner.

JOSEPH R. LIBERMAN, Examiner.

1. A LUBRICANT COMPOSITION CONSISTING ESSENTIALLY OF AN ESTER-BASEDSYNTHETIC FLUID OF LUBRICATING VISCOSITY ABOVE 0.01 TO 5% BY WEIGHT OFPHENOTHIAZINE AND ABOUT 0.01 TO 5% BY WEIGHT OF DIPYRIDYLAMINE ANDSUFFICIENT TO RETARD OXIDATION OF SAID ESTER BASED SYNTHETIC FLUID ATTTEMPERATURES IN EXCESS OF 400*F., SAID ESTER BASED FLUID BEING AN ESTEROF AN ALKANOL OF 4 TO 12 CARBON ATOMS AND AN ALKANE CARBOXYLIC ACID OF 4TO 12 CARBON ATOMS.